Thermostatic control switch



July 11, 1961 L. O. STUTRUD THERMOSTATIC CONTROL SWITCH Filed Sept. 29, 1958 2 Sheets-Sheet 1 VII."

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THERMOSTATIC CONTROL SWITCH 2 Sheets-Sheet 2 INVENTOR.

Lynn 0. Sfufrua BY g z g His After/7e; 2

July 11, 1961 Filed Sept. 29, 1958 w w Q I I /v/ T I 8 w. I WWW L 2 w I I m 1 x I H 2 H I u 6 M I 4 \k 5 4 Ill I 6 I91 6 I 2 G O I F 5 2 I H I 4 4 I F I 3 Ix 4 I I O O 2 95/ United States Patent 2,992,309 THERMOSTATIC CONTROL SWITCH Lynn 0. Stutrud, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Sept. '29, 1958, Ser. No. 764,138 7 Claims. (Cl. 200-138) This invention relates to refrigerating apparatus and more particularly to a thermostatic control switch for use in controlling refrigerating systems and the like.

In a control for a refrigerating system and particularly in controls responsive to evaporator temperature changes it is desirable to provide an inexpensive switch which will respond promptly to changes in evaporator temperature and which will not be unduly influenced by changes in temperature of the air surrounding the switch. In view of the fact that the evaporator of a refrigerating system operates at a temperature below the dew point of the surrounding air it is also necessary that the control switch be not adversely affected by condensation of moisture from the air.

It is an object of this invention to provide a thermostatically operated switch which responds very quickly to temperature changes in a refrigerant evaporator or the like.

Still another object of this invention is to provide a low cost moisture proof switch which will not be affected adversely by condensation of moisture on those portions of the switch exposed to ambient air.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

In the drawings:

FIGURE 1 is a plan view, with parts broken away, of a switch embodying the invention;

FIGURE 2 is a vertical sectional view taken substantially on the line 2-2 of FIGURE 1;

FIGURE 3 is a vertical sectional view taken substantially on line 3--3 of FIGURE 2;

FIGURE 4 is a horizontal sectional view taken substantially on line 4-4 of FIGURE 2;

FIGURE 5 is a horizontal sectional view taken substantially on line 5--5 of FIGURE 2; and

FIGURE 6 is a vertical sectional view showing the switch enclosed within an outer protective housing.

Referring now to the drawings wherein a preferred embodiment of the invention has been shown, reference numeral 10 designates a molded plastic housing element which serves as a support for the various movable elements of the switch and reference numeral 12 designates a metallic plate, preferably of aluminum or some other good conductor of heat, which serves to close the open side of the switch housing 10.

Within the housing 10 there is disposed a bimetallic switch actuator blade 14 which is arranged to lie fiat against the metallic plate 12 in the one extreme position of the bimetallic element as best shown in FIGURE 2. The one end of the bimetallic element 14 is at all times clamped between the plate 12 and the housing 10 by means of the assembly screw 16. The other end of the bimetallic element 14 serves to support an insulating collar or yoke member 18 which is carried by the free end of the bimetallic element 14. The bottom of the yoke member 18 rests on the element 14 and is held in place by means of the struck up cars 20 which are integral with the element 14.

A pair of switch contacts 22 and 24 are provided as shown and serve to make and break the flow of current through the switch. The contact element 24 is carried by and electrically connected to a cantilever type blade spring 26 which has its one end secured to the switch housing ice 10 by means of a terminal screw 28 which also serves to connect the electric lead wire 30 to the blade 26. The contact 22 is carried by and electrically connected to an over-center type of blade spring 34 which has its one end secured to the casing 10 by means of a terminal screw 36 which also serves to connect the electric lead 38 to the fixed end of the spring 34.

The spring 34 is of the well-known type which serves to buckle with a snap movement when the free end of the thermostatic element 14 moves upwardly so as to push the contact 24 against the contact 22 to a point past the over-center position of the spring 34 at which time the contact 22 snaps upwardly out of contact with the contact 24. The snap spring 34, as best shown in FIGURE 5, is provided with a pair of longitudinally extending slots 40 and 42 which serve to provide in effect three separate parallel spring elements 44, 46 and 48. The spring elements 44 and 48 are provided with crimp portions 50 in accordance with well-known practice so as to facilitate the over-center snap movement of the free end of the spring. The center portion 46 of the snap spring is arranged to abut against the lower end of an adjusting screw 52. By adjusting the position of the screw 52 relative to the casing 10 it is possible to adjust the temperature at which the contacts 22 and 24 snap apart.

As best shown in FIGURE 2, the metallic cover plate 12 against which the bimetallic element 14 abuts is arranged in direct contact with a wall element 56 forming a part of the evaporator. By virtue of this structural relationship the switch responds very eifectively and quickly to changes in the temperature of the evaporator. Furthermore the insulating housing 10 which is formed of molded plastic material which is a relatively poor conductor of heat serves to shield the bimetallic element from temperature changes of the air surrounding the evaporator. It should also be noted that there is no direct metallic contact between the bimetallic element and the metallic spring elements 26 and 34 which support the contacts 22 and 24. Furthermore an insulating shield 60 is provided between the bimetallic element 14 and the metallic spring 26 so as to electrically and thermally insulate the bimetallic element 14 from the metallic spring elements 26 and 34.

FIGURE 6 shows the switch assembly described hereinabove disposed within an outer metallic protective housing or can like element 62 which serves to completely enclose the switch assembly. A moisture impervious sealing compound 64 such as epoxy resin is poured into the open end of the metallic housing or can 62 so as to not only hold the switch assembly in place within the can but also so as to completely protect the inner switch housing from the ingress of any moisture from the air surrounding the can.

It will be noted that in the arrangement shown in FIGURE 6 the metallic plate element 12 of the thermostatic control switch is arranged in direct contact with one wall of the can 62 which wall is in turn in direct contact with the evaporator portion 56. By virture of the above described arrangement a very inexpensive but completely moisture-proof switch has been provided which responds very quickly to temperature changes within an evaporator or the like.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, as may come within the scope of the claims which follow.

What is claimed is as follows:

1. In a snap switch, a metallic base member, a molded plastic housing having an open side arranged to be closed by said metallic base member, circuit making and breaking switch means carried by said housing, a bimetallic switch actuating member having its one end clamped between said housing and said base member and extending substantially parallel to and in thermal exchange relationship with said metallic base member, said bimetallic member having an insulated yoke means on its free end for actuating said switch means for making and breaking a circuit in response to changes in temperature of said metallic base member, said switch means comprising a pair of cantilever springs having their free ends disposed within said yoke member, one of said springs including means for buckling the same with a snap action toward and away from the other of said springs in response to movement of its free end, and switch contacts carried by the free ends of said cantilever springs.

2. In a snap switch, a metallic base member, a molded plastic housing having an open side arranged to be closed by said metallic base member, switch means carried by said housing, a bimetallic actuator having its one end clamped between said housing and said base member and extending substantially parallel to and in contacting arrangement with said metallic base member, said switch means comprising a first blade spring having its one end secured to said housing and having its free end provided with a contact arranged adjacent the free end of said himetallic actuator and a second blade spring type overcenter snap spring having its one end secured to said housing and having a contact adjacent its free end arranged to be engaged by said first named contact in one position of said over-center snap spring, said bimetallic actuator having means for shifting the free ends of said springs in response to changes in temperature of said metallic base member.

3. In a thermostatically operated switch, a casing of molded insulating material, said casing having one side open, a heat conducting plate arranged to close said open side, a bimetallic thermostat element arranged in abutting relationship with said plate so as to respond to changes in temperature of said plate, switch means carried by said casing and including contacts disposed within said casing and arranged to be actuated by said bimetallic element, an outer metallic casing surrounding said first named casing and having one wall in abutting relationship with said metallic plate, and moisture impervious sealing material in said outer casing filling the voids between said outer casing and said insulating material and sealing the joint between said insulating material and said metallic plate.

4. In a thermostatically operated switch, a casing of molded insulating material, said casing having one side open, a heat conducting plate arranged to close said open side, a bimetallic thermostat element arranged in abutting relationship with said plate so as to respond to changes in temperature of said plate, switch means carried by said casing and including contacts disposed within said casing and arranged to be actuated by said bimetallic element, an outer metallic casing surrounding said first named casing and having one wall in abutting relationship with said metallic plate, and moisture impervious sealing material in said outer casing filling the voids between said outer casing and said insulating material and sealing the joint between said insulating material and said metallic plate, said outer casing comprising a one-piece open ended can, said switch including electrical conductors extending through the open end of said can and passing through a portion of said sealing material.

5. In combination, a casing element formed of heat and electrical insulating material and having an opening in one side thereof, a metallic wall arranged to close said opening and adapted to be mounted in heat exchange relationship with a refrigerator evaporator or the like, a thin leaf spring operatively supported in cantilever fashion at one end thereof with the other end free to move, said leaf spring comprising a one-piece slotted member having a central strip and two lateral strips, said lateral strips being of a difierent length than said central strip so as to provide for snap action of said leaf spring in response to movement of the free end thereof, an electrical contact carried by the free end of said leaf spring, a second resilient spring am having one end secured to said casing and having a contact at its free end arranged to be engaged by said contact on the free end of said thin leaf spring in one position of said leaf spring, a bimetallic element having its one end anchored between said casing and said plate and having its free end arranged to actuate the free ends of said leaf spring, an abutment for a mid portion of said leaf spring, and means including an actuator outside of said casing element for changing the position of said abutment so as to change the temperature at which said contacts separate.

6. In combination, a casing element formed of heat and electrical insulating material and having an opening in one side thereof, a metallic wall arranged to close said opening and adapted to be mounted in heat exchange relationship with a refrigerator evaporator or the like, a thin leaf spring operatively supported in cantilever fashion at one end thereof with the other end free to move, said leaf spring comprising a one-piece slotted member having a central strip and two lateral strips, said lateral strips being of a different length than said central strip so as to provide for snap action of said leaf spring in response to movement of the free end thereof, an electrical contact carried by the free end of said leaf spring, a second resilient spring arm having one end secured to said casing and having a contact at its free end arranged to be engaged by said contact on the free end of said thin leaf spring in one position of said leaf spring, a bimetallic element having its one end anchored between said casing and said plate and having its free end arranged to actuate the free ends of said leaf spring, an abutment for a mid portion of said leaf spring, and means including an actuator outside of said casing element for changing the position of said abutment so as to change the temperature at which said contacts separate, an open ended metallic can enclosing said casing element, and moisture impervious material closing the open end of said can and sealing the joint between said casing element and said metallic wall.

7. In a thermostatically operated control, a flat metallic temperature sensing base member, a molded plastic housing having an open side arranged to abut one side of said base member, a snap acting circuit making and breaking switch carried within said housing, an elongated bimetallic member having a free end portion extending substantially parallel to and in contacting arrangement with said temperature sensing base member, means carried by said free end arranged for actuating said switch for making and breaking a circuit in response to changes in temperature of said temperature sensing base member, an outer metallic casing surrounding said housing and having one wall thereof arranged in abutting relationship to said base member, and moisture impervious sealing material in said outer casing filling the voids between said outer casing and said housing and sealing the joint between said housing and said base member.

References Cited in the file of this patent UNITED STATES PATENTS 2,098,181 Dillman Nov. 2, 1937 2,262,026 Hastings Nov. 11, 1941 2,471,806 Wilson et a1. May 31, 1949 2,692,317 Bletz Oct. 19, 1954 2,767,284 Moksu Oct. 16, 1956 2,792,473 Hawke May 14, 1957 2,814,704 Bald Nov. 26, 1957 2,824,933 Shanley Feb. 25, 1958 FOREIGN PATENTS 986,351 France Mar. 21, 1951 

